Similar to hypies. When you are really, really excited or hyper, and you're going crazy! The single form of 'gibbies' is gibby. An example of a single gibby is when you are playing nintendo and you get a high score.. but you were already expecting it because you've done it before, but it was hard. Your reaction would be something like, "YES." .. that is using one gibby. However, if you've got the gibbies in the first place... there are usually more than one!
person A: I can't focus!
person B: why?
person A: cause i've got fucking GIBBIES!